Three.js – Rotating a sphere around a certain axis

I have a problem. In Three.js, I want to rotate a sphere (Earth) around axis tilted by 23.5 degs. I found sphere.rotation.x, sphere.rotation.y and sphere.rotation.z, but when I combine them in the correct ratio, the sphere’s rotation is quite weird – it has no permanent rotation axis. I think I need a function like sphere.rotation.vector(1,0,-1). Does anyone know how this function is called and how the correct syntax is?

Many thanks for answers!

Answer

You need to use quaternions for this. This video explains what quaternions are and how they are used in 3D graphics.

You can construct a quaternion like this:

quaternion = new THREE.Quaternion().setFromAxisAngle( axisOfRotation, angleOfRotation );

Then you apply it to your object by:

object.rotation.set( new THREE.Euler().setFromQuaternion( quaternion ) );

You can also achieve this by using object hierarchies. For example, you can make an Object3D() instance and tilt it by 23.5 degs, then create a sphere (Earth) and add it to the tilted object. The sphere will then rotate around the tilted Y axis. Quaternions however, are the best tool for solving this.